Image display devices may be used to project or display a still or video image, or to enable the image to be viewed simultaneously by a large or small audience. Such display devices are intended to produce image color and brightness as faithfully as possible. However, the quality of the projected image often may be enhanced by, among other factors, a brighter light source. The brightness of the light source used may be particularly important when projecting an image in the presence of even moderate ambient light levels.
Projection engines typically modulate red, green, and blue light to produce a projected image, where the red, green, and blue light is derived from a white light source. For example, the white light produced by the light source may be focused and directed sequentially onto color filters, such as a color wheel or color drum. A color wheel is typically a rapidly rotating color filter wheel interposed between the light source and an image-forming element, and typically includes segments having different light-filtering properties. A typical color wheel may include transmissive or reflective filter segments, such as a red filter segment, a green filter segment, and a blue filter segment. As the color wheel is rapidly rotated, colored light may be sequentially projected onto an image forming apparatus.
While the use of such sequential color filters effectively yields the desired red, green, and blue light for image formation, it typically does so by blocking the transmission of undesired light wavelengths. In other words, to produce colored light, a significant portion of the light from the light source may be blocked, resulting in a decreased light output of the light engine, compared to the output of the light source.
In addition, the use of a color filter wheel may require that the wheel be rotated at very high speeds (for example, up to 7,500 rpm), and with high precision. Such a mechanism typically is not only expensive, but is delicate, and may create noise during operation of the projector.